John Fletcher wrote:
A lady on the production line in a factory where I used to work
(electronic assembly, not a noisy environment) had a constant "popping"
noise in her ears. It was at about heart rate, don't know whether it was
synchronised. If you placed your ear next to hers, you could hear it
too. Must have been hell to live with. The noise, not the lady.

I've had a hair in my ear canal rub against my eardrum
with similar results.